An organic EL element includes a pair of electrodes (anode and cathode) and a light-emitting layer placed between the electrodes as main components. The organic EL element is substantially characterized in that organic compounds are used as materials for the light-emitting layer. The organic EL element emits light of certain color and intensity by application of a voltage between the electrodes.
In order to improve characteristics such as the intensity and spectral width of light emitted from the organic EL element, use of an optical resonance phenomenon has been investigated. For example, proposed is a so-called single-photon type organic EL element in which a transparent electrode, a single light-emitting layer, and a back electrode are stacked in this order on a transparent substrate. In this organic EL element, a semitransparent reflective film is provided between the transparent substrate and the transparent electrode, and an optical micro resonator is configured thereinside by setting an optical distance between the semitransparent reflective film and the back electrode to one wavelength or an integral multiple of one wavelength (see, for example, Patent Literature 1).
Further, it has been proposed that in a multi-photon type organic EL element in which a plurality of light-emitting units are stacked with an intermediate unit placed therebetween, each of the light-emitting units is disposed at such a position that beams of light emitted from the light-emitting units each resonate to improve light-emitting characteristics of the organic EL element. Specifically, an organic EL element has been proposed in which an optical distance between the light-emitting position of each light-emitting unit and an anode which reflects light is set so as to cause an optical resonance phenomenon, whereby the light-emitting units each satisfy optical resonance conditions (see, for example, Patent Literature 2).